Make default visibility collapsed when there is no binding element

Question

I have a user control with textbox and button which are bound to properties from viewmodel.

    <Grid>
        <StackPanel>
            <TextBox Text=" Hi" IsEnabled="{Binding IsReadOnly, UpdateSourceTrigger=PropertyChanged}"></TextBox>
            <Button Content="B" Visibility="{Binding IsVisible, UpdateSourceTrigger=PropertyChanged, Converter={StaticResource BooleanToVisibilityConverter}}"></Button>
        </StackPanel>
    </Grid>

How to make the button invisible when the datacontext is not provided for this usercontrol?

Answer 1

FallbackValue

<Button Content="B" Visibility="{Binding IsVisible,
                                 UpdateSourceTrigger=PropertyChanged,  
                                 Converter={StaticResource BooleanToVisibilityConverter}}, 
                                 FallbackValue=Collapsed"></Button>